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J. Chem. Eng. Data 2000, 45, 1016-1018
Excess Molar Enthalpies of Binary Mixtures Containing N,N-Dimethylformamide + Six 2-Alkanols (C3-C8) at 300.15 K H. Iloukhani,* J. B. Parsa, and A. A. Saboury Department of Chemistry, Faculty of Science, Bu-Ali-Sina University, Hamadan, Iran
Excess molar enthalpies, HEm, of N,N-dimethylformamide + 2-propanol, + 2-butanol, + 2-pentanol, + 2-hexanol, + 2-heptanol, and + 2-octanol have been determined at 300.15 K and atmospheric pressure using an isothermal microcalorimeter. HEm values are positive over the entire range of composition of N,N-dimethylformamide and increase in the order 2-propanol < 2- butanol < 2-pentanol < 2-hexanol < 2-heptanol < 2-octanol. Maximum values of HEm vary from 500 J‚mol-1 up to 900 J‚mol-1. The results are explained in terms of the strong self-association exhibited by the 2-alkanols and the cross-association of the O‚‚‚HO specific interaction. The Redlich-Kister equation, fitted to the experimental results, provides a satisfactory mathematical representation of HEm in all mixtures.
Introduction The present work forms part of a program involved in the study of the thermodynamic behavior of some binary mixtures in which specific interactions between unlike molecules can occur (Iloukhani, 1997; Iloukhani and Parsa, 1998; Iloukhani and Ghorbani, 1998; Iloukhani et al., 1999). We have determined the experimental excess molar enthalpies, HEm, of N,N-dimethylformamide (DMF) + six 2-alkanols, namely, 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, 2-heptanol, and 2-octanol at 300.15 K. Experimental values have been fitted to the RedlichKister (1948) equation to determine the binary coefficients and standard deviation. A qualitative discussion of the results is given. To our knowledge, mixtures of DMF with 2-alkanols have not been previously studied. Experimental Section Materials. Characterization data for DMF and the 2-alkanols are listed in Table 1. N,N-Dimethylformamide was purified by the standard method described by Perrin and Armarego (1970). All 2-alkanols used were purified by distillation using a 10 m fractionation column. The purified compounds were stored in brown glass bottles and fractionally distilled immediately before use. The purity of each compound was ascertained by the constancy of the boiling point and also from the density and refractive index, which agreed, as shown in Table 1, with the literature values (Riddick and Bunger, 1970; Weast, 1990). The densities were measured at 293.15 K using a bicapillary pycnometer with an uncertainty of 5 parts in 105. Refractive indices were measured at 293.15 K with an Abbe´ refractometer. Water was circulated to the refractometer from a constanttemperature bath at 293.15 K. The uncertainty of the refractive index measured is on the order of (0.0002. Apparatus and Procedure. Excess molar enthalpies, HEm, were determined using an isothermal microcalorimeter (Thermal Activity Monitor, TAM, model 2277, Thermometric, Sweden). It was equipped with four channels, allowing for the rate of heat output. Each channel of the calorimeter was independently electronically calibrated * E-mail:
[email protected].
Table 1. Sources, Purity Grades, Densities, G, and Refractive Indices, nD, of Pure Components and Comparison with Literature Values at 293.15 K F/g‚cm-3
purity component source mass % DMF 2-propanol 2-butanol 2-pentanol 2-hexanol 2-heptanol 2-octanol a
Merck Merck Merck Merck Merck Merck Merck
99.8 99.7 99.5 >98 >98 >99 >98
nD
exp
lit.
exp
lit.
0.948 62 0.785 61 0.807 01 0.809 53 0.816 84 0.817 24 0.819 11
0.94873a 0.78545a 0.8069a 0.8094a 0.8167b 0.8171a 0.8193b
1.430 29 1.377 31 1.397 31 1.406 59 1.414 56 1.421 25 1.420 19
1.43047a 1.37720a 1.3972a 1.4064a 1.4144b 1.4210b 1.4203b
Riddick and Bunger, 1970. b Weast, 1990.
with a precision of (0.2%. Each channel is a twin heatconduction calorimeter, where the heat-flow sensor is a semiconductor thermopile (multijunction thermocouple plates) positioned between the vessel made from stainless steel. The insertion vessel was also made from stainless steel. The rate of heat output from the sample cell with respect to the reference cell, displayed digitally, was recorded with an accuracy of 0.1 µW by a DIGITAM 3 computer program. The microcalorimetric experiments were performed at a fixed temperature of (300.15 ( 0.01 K). The uncertainty in mole fraction is estimated to be (1 × 10 -4 and was determined from weighing the pure components and pump reservoir. These uncertainties were also based on the assumption that the pump could deliver steady flow to at least the same uncertainty as (1 × 10 -4 mole fraction. The average uncertainty in HEm was estimated to be 1%. Before measurement, the calorimeter was checked using the test mixture cyclohexane + hexane, for which literature values are well-known (Gmehling, 1993), and agreement between ours and literature data was better than 0.6% over the central range of mole fraction of cyclohexane. Results and Discussion The measured excess molar enthalpies, HEm, of N,Ndimethylformamide + 2-propanol, + 2-butanol, + 2-pentanol, + 2-hexanol, + 2-heptanol, and + 2-octanol at 300.15
10.1021/je000151h CCC: $19.00 © 2000 American Chemical Society Published on Web 08/26/2000
Journal of Chemical and Engineering Data, Vol. 45, No. 6, 2000 1017 -1 Table 2. Excess Molar Enthalpies, HE m (J‚mol ), for Binary Mixtures of N,N-Dimethylformamide + 2-Alkanols at 300.15 K
x
HEm
0.0537 0.1455 0.2211 0.2846 0.3381 0.3844
51.1 141.6 220.8 294.6 348.6 394.2
xDMF + (1 - x)2-Propanol -0.2 0.4246 432.5 -6.7 0.7129 338.8 0.8 0.4599 463.6 -0.24 0.7766 265.1 1.5 0.4911 488.1 10 0.8528 185.8 3.5 0.5721 493.4 17.6 0.9455 95.3 -4.2 0.6124 458.4 5.8 -8.2 0.6589 392.8 -17.3
0.0638 0.1697 0.2541 0.3229 0.3801 0.4284
78.7 180.7 278.3 356.9 422.7 476.4
0.6 -6.8 8.1 -7.5 0.0 -7.8
0.0748 0.1951 0.2878 0.3613 0.4211 0.4706
90.7 206.8 309.3 396.1 480.7 552.5
xDMF + (1 - x)2-Pentanol 0.2 0.5123 601.9 5.7 0.7795 1.7 0.5480 644.9 -4.1 0.8319 -5.3 0.5787 674.0 -15.2 0.8912 1.3 0.6556 654.9 0.4 0.9612 3.8 0.6923 624.0 6.7 3.2 0.7333 581.9 8.3
98.2 246.2 372.2 470.2 555.3 621.0
xDMF + (1 - x)2-Hexanol -0.1 0.5491 677.2 -0.3 0.8039 1.3 0.5842 720.3 3.1 0.8516 -2.6 0.6143 745.7 3.3 0.9053 -0.8 0.6872 751.2 1.4 0.9663 2.8 0.7228 716.1 10.3 1.1 0.7612 670.5 3.8
0.0952 0.2399 0.3448 0.4242 0.4864 0.5365
135.9 290.2 414.9 519.5 608.5 678.2
xDMF + (1 - x)2-Heptanol 0.0 0.5777 732.7 -0.4 0.8215 0.7 0.6122 778.5 -0.8 0.8657 -1.7 0.6414 806.0 -5.3 0.9148 -1.9 0.6666 820.7 -9.3 0.9699 4.7 0.7455 816.7 11.7 4.0 0.7817 752.1 9.6
0.1055 0.2613 0.3709 0.4522 0.5149 0.5647
xDMF + (1 - x)2-Octanol 153.8 0.1 0.6052 799.1 7.6 0.8377 323.5 -1.9 0.6389 843.3 2.9 0.8784 475.3 10.7 0.6672 875.9 -1.8 0.9233 576.5 -15.7 0.7353 904.8 -7.1 0.9731 669.1 -2.9 0.7665 874.7 -9.4 742.7 8.0 0.8005 820.2 3.1
0.0857 0.2194 0.3190 0.3960 0.4574 0.5075
δHEm
x
HEm
δHEm
x
xDMF + (1 - x)2-Butanol 0.4697 522.3 -8.7 0.7488 0.5054 559.4 -4.0 0.8067 0.5366 588.7 4.8 0.8743 0.6161 604.5 13.2 0.9542 0.6548 567.4 -2.9 0.6986 521.5 -7.3
HEm
467.9 372.9 263.4 124.5
δHEm -7.2 0.7 4.9 -0.7
5.2 -0.2 1.7 0.3
532.5 0.8 471.4 -12.7 345.8 5.5 158.9 -0.4
∑A (1 - 2x) i
which is evaluated from the equation
σ(HEm) ) |φ/(n - p)|0.5 607.5 495.4 364.7 185.1
11.6 2.5 4.3 0.4
635.4 507.7 386.0 205.1
715.3 564.5 415.5 228.3
-7.7 -7.9 5.1 -0.4
9.4 0.0 -2.9 0.3
i-1
(1)
where x is the mole fraction of DMF and Ai are the coefficients for the binary mixtures. They are presented in Table 3 together with the standard deviation σ(HEm),
(2)
where n is the number of the experimental points and p is the number of adjustable parameters Ai. φ is the objective function defined as
φ)
K are listed in Table 2, together with the deviations, δ(HEm), and are shown qraphically in Figure 1. The results were fitted to the Redlich-Kister (R-K) polynomial
HEm/(J‚mol-1) ) x(1 - x)
Figure 1. Excess molar enthalpies for the binary mixtures of (x)N,N-dimethylformamide + (1 - x)2-alkanols at 300.15 K.
∑δ (H 2
E m)
(3)
where E E - Hm,cal δ(HEm) ) Hm,exp
The HEm values for the binary mixture are positive for all the systems. The maxima vary from 500 J‚mol-1 up to 900 J‚mol-1 and increase in the order 2-propanol to 2-octanol. These positive values suggest that the structure-breaking effect of the components is dominant in the mixtures and associations of pure 2-alkanols, owing to strong hydrogen bonding between molecules. The complex molecular interactions in these systems make difficult even a qualitative interpretation of the results. In fact, in addition to the H-bond association between DMF molecules, the H-bond association of 2-alkanols with the DMF considerably affects the properties of the mixtures with endothermic as well as exothermic contributions. Acknowledgment We are thankful to Bu-Ali-Sina University for providing the necessary facilities to carry out the work.
Table 3. Values of the Adjustable Coefficients, Ai, in Eq 1 and the Standard Deviation, σ(HE m), in Eq 2 for N,N-Dimethyformamide + Alkanols at 300 K DMF + Ai, σ A1 A2 A3 A4 A5 A6 A7 A8 σ
2-propanol
2-butanol
2-pentanol
2-hexanol
2-heptanol
2-octanol
1922.8 -511.4 -2388.4 1514.7 2237.8 -1855.3
2236.9 -1648.7 -1623.7 3072.4 1718.7 -2553.6
2447.2 -2785.3 2011.0 3163.3 -7406.2 -2761.9 7737.5
9.8
7.8
2373.8 -2377.7 -1222.0 4602.3 2654.2 -7586.5 -689.8 3922.6 9.0
2490.2 -2770.6 3328.1 -2802.2 -7925.6 17134.4 6700.9 -16689.2 8.2
2615.2 -2444.9 2018.9 -11137.6 4376.2 44504.5 -8506.7 -42533.5 9.7
6.0
1018
Journal of Chemical and Engineering Data, Vol. 45, No. 6, 2000
Literature Cited Gmehling, J. Excess Enthalpies for 1,1,1-Trichloroethane with Alkanes, Ketones, and Esters. J. Chem. Eng. Data 1993, 38, 143-146. Iloukhani, H. Excess Molar Enthalpies for Binary Mixtures with Trichloroethylene + Alkan-1-ols (C3-C8) at 298.15 K. J. Chem. Eng. Data 1997, 42, 802-805. Iloukhani, H.; Ghorbani, R. Volumetric Properties of N,N-Dimethylfomamide with 1,2-Alkanodiols at 20 °C. J. Solution Chem. 1998, 27, 141-149. Iloukhani, H.; Parsa, J. B. Enthalpies of Mixing for the Binary Mixtures of Tetrachloroethylene with Some Alkan-1-ols (C3-C8) at 298.15 K. J. Phys. Chem. Liq. 1998, 36, 141-147. Iloukhani, H.; Parsa, J. B.; Azizian, S. Ultrasonic Studies for Binary Mixtures wirh Trichloroethylene + Alkan-1-ols (C3-C8) at 303.15 K. J. Chem. Eng. Data 1999, 44, 152-154.
Perrin, D. D.; Armarego, W. L. Purification of Laboratory Chemicals, 3rd ed.; Pergamon Press: New York, 1970. Redlich, O. J.; Kister, A. T. Algebraic Representation of Thermodynamic Properties and the Classification of Solutions. Ind. Eng. Chem. 1948, 40 (2), 345-348. Riddick, J. A.; Bunger, W. B. Techniques of Chemistry, 3rd ed.; WileyInterscience: New York, 1970. Weast, C. R. CRC Handbook of Chemistry and Physics, 1st ed.; Chemical Rubber Publishing Co.: Boca Raton, FL, 1990.
Received for review May 22, 2000. Accepted July 7, 2000.
JE000151H
